Imaging apparatus

ABSTRACT

An imaging apparatus includes an optical element configured to separate incident light into light components in at least two types of wavelength bands. The incident light includes light emitted from a narrow-band light source. At least one light component of the light components in the at least two types of wavelength bands separated by the optical element is light in a narrow band separated by a bandwidth corresponding to a width of a wavelength of the light emitted from the narrow-band light source.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to an imaging apparatus.

Description of the Related Art

An imaging apparatus, for example, an endoscopic apparatus hasconventionally mainly used a CCD (Charge Coupled Apparatus) imagesensor. Recently, however, a CMOS (Complementary Metal OxideSemiconductor) image senor is mainly used because of its advantages suchas low cost, single power supply, and low power consumption. As the CMOSimage sensor, a rolling shutter method is often employed in general (seeJapanese Patent Laid-Open No. 2018-175871).

SUMMARY OF THE INVENTION

One of problems to be solved by an embodiment disclosed in thisspecification is to ensure image quality sufficiently for observation.However, the problem is not limited to this, and obtaining functions andeffects derived by configurations shown in an embodiment configured toimplement the present invention to be described later can also bedefined as another problem to be solved by the embodiment disclosed inthis specification and the like.

An imaging apparatus according to an embodiment is an imaging apparatuscomprising, an optical element configured to separate incident lightinto light components in at least two types of wavelength bands, whereinthe incident light includes light emitted from a narrow-band lightsource, and wherein at least one light component of the light componentsin the at least two types of wavelength bands separated by the opticalelement is light in a narrow band separated by a bandwidth correspondingto a width of a wavelength of the light emitted from the narrow-bandlight source.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of the configuration of animaging system including an imaging apparatus according to anembodiment;

FIG. 2 is a view showing some components of an imaging apparatusaccording to a comparative example;

FIG. 3 is a view showing some components of the imaging apparatusaccording to an embodiment;

FIG. 4 is a graph for explaining processing of the imaging apparatusaccording to an embodiment; and

FIG. 5 is a view showing an example of an imaging operation of theimaging apparatus according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

An imaging apparatus according to an embodiment will now be describedwith reference to the accompanying drawings. Note that the embodiment isnot limited to the following contents. In addition, the contentsdescribed in one embodiment or modification are similarly applied toanother embodiment or modification in principle.

FIG. 1 is a block diagram showing an example of the configuration of animaging system 1 including an imaging apparatus 10 according to thisembodiment. As shown in FIG. 1, the imaging system 1 according to thisembodiment includes the imaging apparatus 10, a light source apparatus30, and an optical fiber 31.

The imaging apparatus 10 is used as, for example, a rigid endoscope fora medical application, which is an apparatus that captures the inside ofa subject 100. The imaging apparatus 10 includes a scope 11, a camerahead 12, a camera cable 13, and a CCU (Camera Control Unit) 14. Notethat the imaging apparatus 10 is not limited only to the rigidendoscope.

The scope 11 is inserted into the inside of the subject 100 whenperforming imaging. An objective lens 11 a is provided at the distal endof the scope 11.

The camera head 12 includes a prism 12 a, a plurality of image sensors12 b, 12 c, and 12 d, and an image sensor control circuit 12 e.

The prism 12 a separates incident light into light components in two ormore types of wavelength bands. For example, the prism 12 a spectrallydivides incident light into light in a narrow band and light in awavelength band other than the wavelength band of the light in thenarrow band. More specifically, the prism 12 a spectrally dividesincident light into light in a narrow band, light in a broadband, andlight in an infrared wavelength band. The broadband is a wavelength bandwider than the narrow band, and light in the broadband is light in avisible light band other than the wavelength band of the light in thenarrow band. The prism 12 a is an example of an optical element.

The plurality of image sensors receive the light components in the twoor more types of wavelength bands separated by the prism 12 a,respectively. For example, the plurality of image sensors are CMOS(Complementary Metal Oxide Semiconductor) image sensors. For example, asthe plurality of image sensors, the image sensors 12 b, 12 c, and 12 dreceive the light in the broadband, the light in the narrow band, andthe light in the infrared wavelength band separated by the prism 12 a,respectively. The image sensor 12 b corresponds to, for example, thebroadband (expressed as “Wch (channel)” in FIG. 1), and is provided onthe exit surface of the prism 12 a for spectrally divided light in thebroadband. The image sensor 12 c corresponds to, for example, the narrowband (expressed as “Nch” in FIG. 1), and is provided on the exit surfaceof the prism 12 a for spectrally divided light in the narrow band. Theimage sensor 12 d corresponds to, for example, the infrared wavelengthband (expressed as “IRch” in FIG. 1), and is provided on the exitsurface of the prism 12 a for spectrally divided light in the infraredwavelength band. The image sensors 12 b, 12 c, and 12 d will sometime bereferred to as the image sensor 12 b on the Wch side, the image sensor12 c on the Nch side, and the image sensor 12 d on the IRch side,respectively, hereinafter. The imaging surfaces of the image sensors 12b, 12 c, and 12 d are arranged to almost match the imaging surface of anoptical system including the scope 11. The image sensors 12 b, 12 c, and12 d are examples of an imaging element.

Each of the image sensors 12 b, 12 c, and 12 d includes a plurality ofpixels (imaging pixels). The plurality of pixels are arranged in amatrix on the imaging surface. Under the driving control of the imagesensor control circuit 12 e, each pixel generates a video signal(electrical signal) by receiving light, and outputs the generated videosignal. More specifically, for example, the image sensor 12 b is a colorsensor, and each pixel of the image sensor 12 b receives light in thebroadband, thereby outputting a video signal of a broadband image thatis an RGB image. For example, the image sensor 12 c is a monochromesensor, and each pixel of the image sensor 12 c receives light in thenarrow band, thereby outputting a video signal of a narrow-band image.For example, the image sensor 12 d is a monochrome sensor, and eachpixel of the image sensor 12 d receives light in the infrared wavelengthband, thereby outputting a video signal of an IR image. For example, thecamera head 12 including the image sensors 12 b, 12 c, and 12 d outputsan RGB signal to the CCU 14 via the camera cable 13. Note that an analogvideo signal is output from each of the image sensors 12 b, 12 c, and 12d. Alternatively, if each of the image sensors 12 b, 12 c, and 12 dincorporates an A/D (Analog to Digital) converter (not shown), a digitalvideo signal is output from each of the image sensors 12 b, 12 c, and 12d.

Here, the imaging apparatus 10 according to this embodiment is usedwhen, for example, performing a surgical operation by ICG (IndoCyanineGreen) fluorescence angiography for the subject 100. In this case, ICGis administered to the subject 100. ICG is excited by excitation lightemitted by an IR laser 30 d and emits near-infrared fluorescence (to bereferred to as fluorescence hereinafter) of about 800 to 850 nm. In theICG fluorescence angiography, a filter that cuts excitation light isprovided between the scope 11 and the prism 12 a, and the fluorescenceis received by the image sensor 12 d. That is, the image sensor 12 dreceives the fluorescence based on the excitation light, therebyoutputting a video signal of an IR image.

Each of the image sensors 12 b, 12 c, and 12 d is a rolling shutterimage sensor that repeats, for every frame (image), processing ofsequentially starting exposure, at least on each row, from the first rowto the final row of the plurality of pixels and outputting a videosignal sequentially from a row that has undergone the exposure. Here,exposure means, for example, accumulating charges in the pixels.

The image sensor control circuit 12 e drives and controls the imagesensors 12 b, 12 c, and 12 d based on a control signal output from acontrol circuit 14 a to be described later and various kinds ofsynchronization signals output from a timing signal generation circuit14 f to be described later. For example, if the image sensors 12 b, 12c, and 12 d output analog video signals, the image sensor controlcircuit 12 e appropriately applies a gain (analog gain) to each of theanalog video signals output from the image sensors 12 b, 12 c, and 12 d(amplifies the video signals) based on the control signal and thevarious kinds of synchronization signals, thereby controlling the imagesensors 12 b, 12 c, and 12 d such that the video signals multiplied bythe gain are output to the CCU 14. Alternatively, if the image sensors12 b, 12 c, and 12 d output digital video signals, the image sensorcontrol circuit 12 e appropriately applies a gain (digital gain) to eachof the digital video signals output from the image sensors 12 b, 12 c,and 12 d based on the control signal and the various kinds ofsynchronization signals, thereby controlling the image sensors 12 b, 12c, and 12 d such that the video signals multiplied by the gain areoutput to the CCU 14.

The camera cable 13 is a cable that stores signal lines configured totransmit/receive video signals, control signals, and synchronizationsignals between the camera head 12 and the CCU 14.

The CCU 14 performs various kinds of image processing for a video signaloutput from the camera head 12 to generate image data to be displayed ona display 101, and outputs the image data to the display 101 connectedto the CCU 14. Note that the video signal that has undergone the variouskinds of image processing is image data representing an image to bedisplayed on the display 101.

The CCU 14 includes the control circuit 14 a, a storage control circuit14 b, an image processing circuit 14 c, an image composition circuit 14d, an output circuit 14 e, the timing signal generation circuit 14 f,and a storage circuit 14 g. Note that when the image sensors 12 b, 12 c,and 12 d output analog video signals, the CCU 14 includes an A/Dconverter and the like (not shown) as well. The A/D converter converts,for example, analog video signals output from the image sensors 12 b, 12c, and 12 d into digital video signals.

The control circuit 14 a controls various kinds of constituent elementsof the imaging apparatus 10. For example, the control circuit 14 aoutputs control signals to the image sensor control circuit 12 e, thestorage control circuit 14 b, the image processing circuit 14 c, theimage composition circuit 14 d, the output circuit 14 e, and the timingsignal generation circuit 14 f, thereby controlling the circuits. Thecontrol circuit 14 a loads the control program of the imaging apparatus10, which is stored in the storage circuit 14 g, and executes the loadedcontrol program, thereby executing control processing of controlling thevarious kinds of constituent elements of the imaging apparatus 10.Alternatively, the control circuit 14 a incorporates a storage circuit(not shown) and executes a control program stored in the storagecircuit. The control circuit 14 a is implemented by, for example, aprocessor such as an MPU (Micro-Processing Unit).

The storage control circuit 14 b performs control of storing, in thestorage circuit 14 g, a video signal output from the camera head 12based on a control signal output from the control circuit 14 a andvarious kinds of synchronization signals output from the timing signalgeneration circuit 14 f. In addition, the storage control circuit 14 breads the video signal stored in the storage circuit 14 g from each rowbased on the control signal and the synchronization signals. The storagecontrol circuit 14 b then outputs the read video signal of one row tothe image processing circuit 14 c.

The image processing circuit 14 c performs various kinds of imageprocessing for the video signal output from the storage control circuit14 b based on a control signal output from the control circuit 14 a andvarious kinds of synchronization signals output from the timing signalgeneration circuit 14 f. The image processing circuit 14 c thusgenerates image data representing an image to be displayed on thedisplay 101. That is, the image processing circuit 14 c generates theimage based on the video signal. For example, the image processingcircuit 14 c applies a gain (digital gain) to the video signal outputfrom the storage control circuit 14 b, thereby adjusting the brightnessof the image. The image processing circuit 14 c may perform noisereduction processing of reducing noise or edge enhancement processing ofenhancing edges for the video signal output from the storage controlcircuit 14 b. The image processing circuit 14 c outputs the video signal(image data representing the image to be displayed on the display 101)that has undergone the various kinds of image processing to the imagecomposition circuit 14 d.

The image composition circuit 14 d composites video signals output fromthe image processing circuit 14 c to generate composite image data basedon a control signal output from the control circuit 14 a and variouskinds of synchronization signals output from the timing signalgeneration circuit 14 f. The image composition circuit 14 d outputs thecomposite image data to the display 101. The image processing circuit 14c and the image composition circuit 14 d are examples of processingunits.

For example, the storage control circuit 14 b, the image processingcircuit 14 c, and the image composition circuit 14 d are implemented byone processor such as a DSP (Digital Signal Processor). Alternatively,for example, the storage control circuit 14 b, the image processingcircuit 14 c, the image composition circuit 14 d, and the timing signalgeneration circuit 14 f are implemented by one FPGA (Field ProgrammableGate Array). Note that the control circuit 14 a, the storage controlcircuit 14 b, the image processing circuit 14 c, and the imagecomposition circuit 14 d may be implemented by one processing circuit.The processing circuit is implemented by, for example, a processor.

The output circuit 14 e outputs the composite image data output from theimage composition circuit 14 d to the display 101. The display 101 thusdisplays a composite image represented by the composite image data. Thecomposite image is an example of an image. The output circuit 14 e isimplemented by, for example, an HDMI® (High-Definition MultimediaInterface) driver IC (Integrated Circuit), an SDI (Serial DigitalInterface) driver IC, or the like.

The timing signal generation circuit 14 f unitarily manages variouskinds of timings such as the emission timing of light from the lightsource apparatus 30, the exposure timings and video signal outputtimings of the image sensors 12 b, 12 c, and 12 d, and the controltiming of the storage circuit 14 g by the storage control circuit 14 b.

The timing signal generation circuit 14 f generates various kinds ofsynchronization signals such as a horizontal synchronization signal anda vertical synchronization signal, and other synchronization signalsused to synchronize the entire imaging apparatus 10 based on a clocksignal generated by an oscillation circuit (not shown). The timingsignal generation circuit 14 f outputs the generated various kinds ofsynchronization signals to the image sensor control circuit 12 e, thecontrol circuit 14 a, the storage control circuit 14 b, the imageprocessing circuit 14 c, the image composition circuit 14 d, and theoutput circuit 14 e.

In addition, the timing signal generation circuit 14 f generates a lightsource control signal based on the clock signal and a control signaloutput from the control circuit 14 a. The light source control signal isa control signal used to control light emitted from the light sourceapparatus 30 and also synchronize the entire imaging system 1. Thetiming signal generation circuit 14 f outputs the generated light sourcecontrol signal to the light source apparatus 30.

For example, the light source control signal has a rectangular waveform,and takes two levels (states), that is, high level and low level. Forexample, the light source control signal is a control signal that causesthe light source apparatus 30 to emit light during high level, and stopsemission of light from the light source apparatus 30 during low level.

The storage circuit 14 g is implemented by, for example, a RAM (RandomAccess Memory), a ROM (Read Only Memory), a semiconductor memory elementsuch as a flash memory, a hard disk, an optical disk, or the like. TheROM (or flash memory or hard disk) stores various kinds of programs. Forexample, the ROM stores a control program to be executed by the controlcircuit 14 a. In addition, video signals are temporarily stored in theRAM by the storage control circuit 14 b.

The light source apparatus 30 emits various kinds of light based on thelight source control signal. The light source apparatus 30 includes adriving circuit 30 a, a broadband light source 30 b, a driving circuit30 c, a narrow-band light source 30 d, a driving circuit 30 e, and an IRlight source 30 f.

The driving circuit 30 a performs driving control of driving and turningon the broadband light source 30 b based on the light source controlsignal output from the timing signal generation circuit 14 f. Thebroadband light source 30 b is, for example, a white LED (Light EmittingDiode), and emits white light as light in the broadband under thedriving control of the driving circuit 30 a. The white light is, forexample, visible light. Note that the light in the broadband isseparated by the prism 12 a and received by the image sensor 12 b.

The driving circuit 30 c performs driving control of driving and turningon the narrow-band light source 30 d based on the light source controlsignal output from the timing signal generation circuit 14 f. Thenarrow-band light source 30 d is, for example, a blue LED or a bluelaser, and emits blue light as light in the narrow band under thedriving control of the driving circuit 30 c. The blue light is, forexample, visible light. Note that the light in the narrow band isseparated by the prism 12 a and received by the image sensor 12 c.

The driving circuit 30 e performs driving control of driving the IRlight source 30 f to cause the IR light source 30 f to emit excitationlight based on the light source control signal output from the timingsignal generation circuit 14 f. The IR light source 30 f is, forexample, an IR laser, and emits excitation light under the drivingcontrol of the driving circuit 30 e. Note that ICG is excited by theexcitation light, and fluorescence (fluorescence based on the excitationlight) emitted from the ICG is separated by the prism 12 a and receivedby the image sensor 12 d.

The optical fiber 31 guides the various kinds of light from the lightsource apparatus 30 to the distal end portion of the scope 11 andoutputs the light from the distal end portion of the scope 11.

An example of the configuration of the imaging apparatus 10 of theimaging system 1 according to this embodiment has been described above.An imaging apparatus according to a comparative example will bedescribed here. The imaging apparatus according to the comparativeexample is a general imaging apparatus. For example, the imagingapparatus according to the comparative example does not have thefunctions of the narrow-band light source 30 d, the driving circuit 30c, and the like, and includes a prism 112 a and image sensors 112 b, 112c, and 112 d shown in FIG. 2 in place of the above-described prism 12 aand the image sensors 12 b, 12 c, and 12 d. For example, the prism 112 ais a tricolor separating dichroic prism, and the image sensors 112 b,112 c, and 112 d are monochrome sensors. In the imaging apparatusaccording to the comparative example, when white light is emitted, theimage sensors 112 b, 112 c, and 112 d receive red (R+IR) light, green(G) light, and blue (B) light separated by the prism 112 a, and outputan R signal (video signal of R), a G signal (video signal of G), and a Bsignal (video signal of B), respectively. Hence, the imaging apparatusaccording to the comparative example can acquire an RGB image based onthe R signal, the G signal, and the B signal (RGB signal).

As described above, in the imaging apparatus according to thecomparative example, the imaging target is irradiated with light in thebroadband such as white light, and the image sensors 112 b, 112 c, and112 d receive the light in the broadband separated by the prism 112 a,thereby acquiring an RGB image. Since the emitted white light is lightin the broadband from the blue wavelength band to the infraredwavelength band beyond the red wavelength band, the acquired imageincludes the color components of the imaging target. For this reason,the imaging apparatus according to the comparative example can correctlyreproduce the color of the imaging target. However, the reflection andscattering characteristics of light change depending on the wavelength.For example, the reflection and scattering characteristics of lightchange between the red wavelength band, the green wavelength band, andthe blue wavelength band. Hence, when an image is acquired by emittinglight in the broadband such as white light, the resolution of the imagemay lower due to reflection or scattering of light. For example,concerning the contour of unevenness or the like on the surface of theimaging target, the contrast may lower due to reflection or scatteringof light. Hence, for a user such as a doctor who observes images, imagequality may not be sufficient for observation.

On the other hand, there exists a technique of irradiating an imagingtarget with light in the narrow band to increase the resolution of animage. For example, if an image is acquired by irradiating an imagingtarget with light in the blue wavelength band as light in the narrowband using an LED or a laser, the contrast can be increased concerningthe contour of unevenness or the like on the surface of the imagingtarget. However, if the imaging target is irradiated with light in theblue wavelength band as light in the narrow band, information concerningcolors is only information of blue, and there is no information of othercolors such as red and green. For this reason, if an image is acquiredby irradiating the imaging target with only light in the narrow band,the color of the imaging target cannot correctly be reproduced.

The imaging apparatus 10 according to this embodiment performs thefollowing processing to ensure image quality sufficient for the user toobserve. The imaging apparatus 10 according to this embodiment includesthe prism 12 a. The prism 12 a is an optical element that separatesincident light into light components in two or more types of wavelengthbands. The incident light includes light emitted from the narrow-bandlight source 30 d. At least one light component of the light componentsin two or more types of wavelength bands separated by the prism 12 a islight in the narrow band which is separated by a bandwidth correspondingto the width of the wavelength of light emitted from the narrow-bandlight source 30 d.

Alternatively, the imaging apparatus 10 according to this embodimentperforms the following processing to ensure image quality sufficient forthe user to observe. The imaging apparatus 10 according to thisembodiment includes the prism 12 a, and the plurality of image sensors.The prism 12 a is an optical element that separates incident light intolight components in two or more types of wavelength bands. The pluralityof image sensors are imaging elements that receive the light componentsin two or more types of wavelength bands separated by the prism 12 a,respectively. At least one image sensor of the plurality of imagesensors outputs an RGB image independently. For example, at least oneimage sensor of the plurality of image sensors outputs a narrow-bandimage by receiving light in the narrow band, and at least one otherimage sensor outputs a broadband image that is an RGB image by receivinglight in the broadband that is a wavelength band wider than the narrowband. As the image sensor that receives light in the narrow band forexample, a monochrome image sensor (monochrome imaging element) can beused. In addition, as the image sensor that receives light in thebroadband that is a wavelength band wider than the narrow band, forexample, an RGB color image sensor (color imaging element) can be used.

More specifically, in the imaging apparatus 10 according to thisembodiment, as shown in FIG. 3, the prism 12 a is a prism thatspectrally divides incident light into light in the broadband, light inthe narrow band, and light in the infrared wavelength band, the imagesensor 12 b is a color sensor, and the image sensors 12 c and 12 d aremonochrome sensors. In the imaging apparatus 10 according to thisembodiment, the image sensors 12 b, 12 c, and 12 d receive the light inthe broadband, the light in the narrow band, and the light in theinfrared wavelength band separated by the prism 12 a, and output a videosignal of a broadband image, a video signal of a narrow-band image, anda video signal of an IR image, respectively. Accordingly, in the imagingapparatus 10 according to this embodiment, the image processing circuit14 c acquires an RGB image based on the video signal of the broadbandimage (RGB signal), and generates a display image based on thenarrow-band image and the broadband image. The display image includes,for example, the contour component of the imaging target included in thenarrow-band image, and the color component of the imaging targetincluded in the broadband image or the composite image of the broadbandimage and the narrow-band image.

FIG. 4 is a graph showing an example of the transmission characteristic(spectral transmission characteristic) of light separated by the prism12 a of the imaging apparatus 10 according to this embodiment. FIG. 4shows an example of the relationship between the spectral transmissioncharacteristic to light in the narrow band, the spectral transmissioncharacteristic to light in the broadband, and the spectral transmissioncharacteristic to light in the infrared wavelength band. In FIG. 4, theabscissa represents wavelength [nm]. Additionally, in FIG. 4, a curve C1represents a spectral transmission characteristic to light in the narrowband, a curve C2 represents a spectral transmission characteristic tolight in the broadband, and a curve C3 represents a spectraltransmission characteristic to light in the infrared wavelength band.

The light in the narrow band indicated by the curve C1 is used for, forexample, the contour component of the imaging target. More specifically,several spectral films are provided in the prism 12 a. A wavelengthtransmitted through the spectral films and a reflected wavelength areguided to different optical paths, thereby spectrally dividing bluelight as light in the narrow band from Nch of the prism 12 a. The imagesensor 12 c that is a monochrome sensor receives the light in the narrowband spectrally divided by the prism 12 a, and outputs a video signal ofa narrow-band image. Here, the narrow-band image includes the contourcomponent of the imaging target. Hence, the imaging apparatus 10according to this embodiment can increase the contrast concerning thecontour of unevenness or the like on the surface of the imaging target,and the resolution improves.

Here, the light in the narrow band that has exited from Nch of the prism12 a is light separated by a bandwidth (for example, a half-value width)corresponding to the width of the wavelength of light emitted from thenarrow-band light source 30 d, and the half-value width is set to, forexample, 50 [nm] or less. Note that in this embodiment, a case in whichthe half-value width is set to 50 [nm] or less has been exemplified.However, the half-value width is not limited to this, and may be setwithin a wavelength range corresponding to the emission color of ageneral LED. If a laser is used, the half-value width may be set withina narrow wavelength range such as about 1 [nm] or 10 [nm]. Note that thehalf-value width includes a full width at half maximum and a half widthat half maximum that is ½ the full width at half maximum. In thisembodiment, either is usable.

The light in the broadband indicated by the curve C2 is used for, forexample, the color component of the imaging target. More specifically,light in the broadband is spectrally divided from Wch of the prism 12 a.The image sensor 12 b that is a color sensor receives the light in thebroadband spectrally divided by the prism 12 a, and outputs a videosignal of a broadband image. Here, as shown in FIG. 4, if the light inthe broadband indicated by the curve C2 is light in a visible band otherthan the wavelength band of the light in the narrow band indicated bythe curve C1, the broadband image or the composite image of thebroadband image and the narrow-band image includes the color componentof the imaging target. Hence, the imaging apparatus 10 according to thisembodiment can correctly reproduce the color of the imaging target.

Note that the light in the infrared wavelength band indicated by thecurve C3 is used to, for example, generate a fluorescent image to bedescribed later. More specifically, light in the infrared wavelengthband is spectrally divided from IRch of the prism 12 a. The image sensor12 d that is a monochrome sensor receives the light in the infraredwavelength band spectrally divided by the prism 12 a, and outputs avideo signal of an IR image. Here, a portion with a brightness equal toor larger than a threshold exists in the IR image, and the fluorescentimage to be described later is generated based on this portion.

FIG. 5 is a view showing an example of an imaging operation of theimaging apparatus 10 according to this embodiment. FIG. 5 shows anexample of the relationship between the emission timings of white light,blue light, and excitation light emitted from the light source apparatus30, the exposure timings of the rows of the plurality of pixels providedin the image sensors 12 b, 12 c, and 12 d of the imaging apparatus 10,the output timings of video signals output from the image sensors 12 b,12 c, and 12 d, and the output timings of a video signal output from theoutput circuit 14 e. In FIG. 5, the abscissa represents time. In thisembodiment, the frame rate of a video signal (image) output from theimaging apparatus 10 to the display 101 is 60 [fps], and the read periodis 1/60 [s]. That is, the period of outputting a video signal of oneframe from the imaging apparatus 10 to the display 101 and the readperiod are 1/60 [s].

First, at the start of imaging, the control circuit 14 a outputs acontrol signal to the timing signal generation circuit 14 f to cause itto output a first light source control signal that causes the broadbandlight source 30 b to continuously emit white light. The timing signalgeneration circuit 14 f outputs the first light source control signal tothe driving circuit 30 a based on the control signal, and the drivingcircuit 30 a drives the broadband light source 30 b based on the firstlight source control signal, thereby causing the broadband light source30 b to continuously emit white light.

Also, at the start of imaging, the control circuit 14 a outputs acontrol signal to the timing signal generation circuit 14 f to cause itto output a second light source control signal that causes thenarrow-band light source 30 d to continuously emit blue light. Thetiming signal generation circuit 14 f outputs the second light sourcecontrol signal to the driving circuit 30 c based on the control signal,and the driving circuit 30 c drives the narrow-band light source 30 dbased on the second light source control signal, thereby causing thenarrow-band light source 30 d to continuously emit blue light.

Additionally, at the start of imaging, the control circuit 14 a outputsa control signal to the timing signal generation circuit 14 f to causeit to output a third light source control signal that causes the IRlight source 30 f to continuously emit excitation light. The timingsignal generation circuit 14 f outputs the third light source controlsignal to the driving circuit 30 e based on the control signal, and thedriving circuit 30 e drives the IR light source 30 f based on the thirdlight source control signal, thereby causing the IR light source 30 f tocontinuously emit excitation light.

For example, in the first frame, during the read period of 1/60 [s] fromtime T1 to time T2, exposure is sequentially started on each row fromthe first row to the final row of the plurality of pixels of each of theimage sensors 12 b, 12 c, and 12 d. More specifically, the controlcircuit 14 a outputs a control signal to the image sensor controlcircuit 12 e to cause each of the image sensors 12 b, 12 c, and 12 d tooutput a video signal during the read period of 1/60 [s]. The imagesensor control circuit 12 e drives and controls the image sensors 12 b,12 c, and 12 d based on the control signal. As a result, during the readperiod of 1/60 [s], the image sensor 12 b receives light in thebroadband and outputs video signals from all rows as a video signal “W1”of a broadband image. The image sensor 12 c receives light in the narrowband and outputs video signals from all rows as a video signal “B1” of anarrow-band image. The image sensor 12 d receives light in the infraredwavelength band and outputs video signals from all rows as a videosignal “IR1” of an IR image. In this case, the video signal “W1” of thebroadband image, the video signal “B1” of the narrow-band image, and thevideo signal “IR1” of the IR image are output from the image sensors 12b, 12 c, and 12 d, respectively. The video signal “W1” of the broadbandimage is a signal output from the image sensor 12 b that has receivedthe white light. The video signal “B1” of the narrow-band image is asignal output from the image sensor 12 c that has received the bluelight. The video signal “IR1” of the IR image is a signal output fromthe image sensor 12 d that has received fluorescence based on theexcitation light.

Next, in the second frame, during the read period of 1/60 [s] from timeT2 to time T3, the image sensors 12 b, 12 c, and 12 d output videosignals as a video signal “W2” of a broadband image, a video signal “B2”of a narrow-band image, and a video signal “IR2” of an IR image,respectively. In this case, the video signal “W2” of the broadbandimage, the video signal “B2” of the narrow-band image, and the videosignal “IR2” of the IR image are output from the image sensors 12 b, 12c, and 12 d, respectively.

Here, the video signals output from the image sensors 12 b, 12 c, and 12d are changed to the display image of the first frame via the imageprocessing circuit 14 c and the image composition circuit 14 d in theCCU 14, and quickly output from the output circuit 14 e to the display101. More specifically, the image processing circuit 14 c generates afirst display image based on the broadband image represented by thevideo signal “W1” and the narrow-band image represented by the videosignal “B1”. The first display image includes, for example, theresolution component of the imaging target included in the narrow-bandimage, and the color component of the imaging target included in thebroadband image or the composite image of the broadband image and thenarrow-band image. Next, the image composition circuit 14 d extracts, asa target, a portion with a brightness equal to or larger than athreshold from, for example, the IR image represented by the videosignal “IR1”, and generates a fluorescent image that is a marker formedby adding a fluorescent color to the extracted portion. The fluorescentcolor is a color assigned to represent fluorescence when the marker(fluorescent image) is generated, and shows, for example, green of highsaturation. The image composition circuit 14 d superimposes thegenerated fluorescent image on the first display image generated by theimage processing circuit 14 c, thereby generating a second displayimage. The second display image generated by the image compositioncircuit 14 d is output from the output circuit 14 e to the display 101during the period of 1/60 [s]. From the second frame as well, processingsimilar to the above-described processing is performed.

Note that in this embodiment, as the first display image generated bythe image processing circuit 14 c, the video signal of the first displayimage represents the composite signal of the video signal “W1” of thebroadband image and the video signal “B1” of the narrow-band image.Here, if the video signal “W1” of the broadband image (color image) issimply defined as the color image W1, and the video signal “B1” of thenarrow-band image is simply defined as the narrow-band image B1,composition of the color image W1 and the narrow-band image B1 is asfollows. First, a contour image D1 is generated based on the narrow-bandimage B1. The contour image D1 is a signal having a positive/negativevalue whose average value is 0. For example, the contour image D1 isobtained by extracting a frequency component more than a certainfrequency band from the narrow-band image B1 using a high-frequencyextraction filter (HPF). The composite formula at this time isrepresented by W1+D1×K. A coefficient K represents the strength of acontour. The larger the coefficient K is, the stronger the contour ofthe color image is. For example, the coefficient K may be arbitrarilyadjustable by the user.

As described above, in the imaging apparatus 10 according to thisembodiment, the imaging target is irradiated with light in the bluewavelength band as light in the narrow band, and the image sensor 12 creceives the light in the narrow band separated by the prism 12 a,thereby acquiring the narrow-band image. Also, in the imaging apparatus10, the imaging target is irradiated with light in the broadband such aswhite light, and the image sensor 12 b receives the light in thebroadband separated by the prism 12 a, thereby acquiring the broadbandimage (RGB image). Furthermore, in the CCU 14, the display image isgenerated based on the narrow-band image and the broadband image. Here,the display image includes the contour component of the imaging targetincluded in the narrow-band image. For this reason, according to theimaging apparatus 10 of this embodiment, it is possible to increasecontrast concerning the contour of unevenness or the like on the surfaceof the imaging target, and the resolution improves. In addition, thedisplay image includes the color component of the imaging targetincluded in the broadband image or the composite image of the broadbandimage and the narrow-band image. For this reason, according to theimaging apparatus 10 of this embodiment, it is possible to correctlyreproduce the color of the imaging target. Hence, in this embodiment,image quality sufficient for the user to observe can be ensured.

The imaging apparatus 10 according to this embodiment includes the prism12 a that separates incident light into light components in two or moretypes of wavelength bands. More specifically, the imaging apparatus 10according to this embodiment uses the prism 12 a that spectrally dividesincident light into light in the narrow band and light in the broadband.Hence, in this embodiment, for example, in the camera head 12, the prism112 a (tricolor separating dichroic prism) according to the comparativeexample need only be changed to the prism 12 a, and it is possible toimplement circuits and apparatuses of a scale similar to the comparativeexample.

The reason why light in the blue wavelength band is selected as light inthe narrow band in this embodiment will be described here using anexamination result.

It is generally known that when an image is acquired using light in theblue wavelength band, the contrast is high concerning unevenness on thesurface of the imaging target. It is also known that when an image isacquired using light in the red wavelength band, the contrast is lowbecause of large transmission or scattering of the red component.Contrast and the like were actually examined using the prism 112 a shownin FIG. 2. More specifically, a “palm” was used as an imaging target,and contrast and the like were examined in a case where a filterconfigured to pass light in the red wavelength band was arranged infront of the incident surface of the prism 112 a shown in FIG. 2, andimages were acquired from R+IRch of the prism 112 a and in a case whereimages were acquired from R+IRch of the prism 112 a without arrangingthe filter. Similarly, contrast and the like were examined in a casewhere a filter configured to pass light in the green wavelength band wasarranged in front of the incident surface of the prism 112 a, and imageswere acquired from Gch of the prism 112 a and in a case where imageswere acquired from Gch of the prism 112 a without arranging the filter.Similarly, contrast and the like were examined in a case where a filterconfigured to pass light in the blue wavelength band was arranged infront of the incident surface of the prism 112 a, and images wereacquired from Bch of the prism 112 a and in a case where images wereacquired from Bch of the prism 112 a without arranging the filter.

As the result of examinations, as for, for example, the tint of thesurface of the “palm” (for example, shades or tones of colors by bloodvessels or the like), it was confirmed that images acquired using lightin the green wavelength band were more easily visible than imagesacquired using light in the red or blue wavelength band. As forunevenness on the surface of the “palm”, it was confirmed that imagesacquired using light in the blue wavelength band had higher contrastthan images acquired using light in the red or green wavelength band.Also, as a result of narrowing the wavelength band, it was confirmedthat contrast improved in all of images acquired using light in the redwavelength band, images acquired using light in the green wavelengthband, and images acquired using light in the blue wavelength band. Atthis time, in a case where light in the red wavelength band was used, abandpass filter having a center wavelength of 607 [nm] and a half-valuewidth of 42 [nm] was used as the filter arranged in front of theincident surface of the prism 112 a. In a case where light in the greenwavelength band was used, a bandpass filter having a center wavelengthof 534.5 [nm] and a half-value width of 48 [nm] was used. In a casewhere light in the blue wavelength band was used, a bandpass filterhaving a center wavelength and a half-value width of 35 [nm] was used.Hence, the transmission characteristics (half-value widths) of thefilters were almost 50 [nm] or less.

Hence, in this embodiment, Nch is assigned to the prism 12 a shown inFIGS. 1 and 3 to improve the contrast, and light in the blue wavelengthband of the highest contrast is selected as the light in the narrowband. That is, in the imaging apparatus 10 according to this embodiment,as an example, the imaging target is irradiated with light in the bluewavelength band as light in the narrow band, and the image sensor 12 creceives the light in the narrow band separated by the prism 12 a toacquire a narrow-band image, thereby improving the contrast.

Note that in this embodiment, a case in which the prism 12 a thatspectrally divides incident light into light in the broadband, light inthe narrow band, and light in the infrared wavelength band is used asthe optical element that spectrally divides incident light into lightcomponents in two or more types of wavelength bands has been described.That is, a case in which Wch, Nch, and IRch are assigned to the prism 12a, as shown in FIGS. 1 and 3 has been described. However, the opticalelement described in the embodiment is not limited to this. For example,if it is possible to improve contrast and correctly reproduce the colorof the imaging target by the configuration of this embodiment, the prism12 a that spectrally divides incident light into light in the broadbandand light in the narrow band may be used as the optical element thatspectrally divides incident light into light components in two or moretypes of wavelength bands. That is, only Wch and Nch may be assigned tothe prism 12 a without assigning IRch.

According to at least one embodiment described above, it is possible toensure image quality sufficiently for the user to observe.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2019-151777, filed Aug. 22, 2019, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An imaging apparatus comprising, an opticalelement configured to separate incident light into light components inat least two types of wavelength bands, wherein the incident lightincludes light emitted from a narrow-band light source, and wherein atleast one light component of the light components in the at least twotypes of wavelength bands separated by the optical element is light in anarrow band separated by a bandwidth corresponding to a width of awavelength of the light emitted from the narrow-band light source. 2.The apparatus according to claim 1, wherein the optical elementseparates the incident light into the light in the narrow band and lightin a wavelength band other than a wavelength band of the light in thenarrow band.
 3. The apparatus according to claim 1, wherein the opticalelement separates the incident light into the light in the narrow band,light in a visible light band other than a wavelength band of the lightin the narrow band, and light in an infrared wavelength band.
 4. Theapparatus according to claim 1, further comprising a plurality ofimaging elements configured to receive the light components in the atleast two types of wavelength bands separated by the optical element,respectively, wherein at least one imaging element of the plurality ofimaging elements outputs a narrow-band image by receiving the light inthe narrow band, and at least one other imaging element outputs abroadband image by receiving light in a broadband that is a wavelengthband wider than the narrow band.
 5. The apparatus according to claim 4,wherein of the imaging elements, the imaging element that receives thelight in the narrow band is a monochrome imaging element.
 6. Theapparatus according to claim 4, wherein of the imaging elements, theimaging element that receives the light in the broadband is a colorimaging element.
 7. The apparatus according to claim 4, furthercomprising a processing unit configured to generate a display imagebased on the narrow-band image and the broadband image.
 8. The apparatusaccording to claim 7, wherein the display image includes a contourcomponent of an imaging target included in the narrow-band image, and acolor component of the imaging target included in the broadband image orin a composite image of the broadband image and the narrow-band image.